Bonding Characteristics and Chemical Inertness of Zr – Si – N Coatings with a High Si Content in Glass Molding

High-Si-content transition metal nitride coatings, which exhibited an X-ray amorphous phase, were proposed as protective coatings on glass molding dies. In a previous study, the Zr–Si–N coatings with Si contents of 24–30 at.% exhibited the hardness of Si3N4, which was higher than those of the middle-Si-content (19 at.%) coatings. In this study, the bonding characteristics of the constituent elements of Zr–Si–N coatings were evaluated through X-ray photoelectron spectroscopy. Results indicated that the Zr 3d5/2 levels were 179.14–180.22 and 180.75–181.61 eV for the Zr–N bonds in ZrN and Zr3N4 compounds, respectively. Moreover, the percentage of Zr–N bond in the Zr3N4 compound increased with increasing Si content in the Zr–Si–N coatings. The Zr–N bond of Zr3N4 dominated when the Si content was >24 at.%. Therefore, high Si content can stabilize the Zr–N compound in the M3N4 bonding structure. Furthermore, the thermal stability and chemical inertness of Zr–Si–N coatings were evaluated by conducting thermal cycle annealing at 270 ◦C and 600 ◦C in a 15-ppm O2–N2 atmosphere. The results indicated that a Zr22Si29N49/Ti/WC assembly was suitable as a protective coating against SiO2–B2O3–BaO-based glass for 450 thermal cycles.


Introduction
Glass molding [1][2][3] has become a vital technique to fabricate aspherical lenses utilized as optical elements for image capture systems in cameras and mobile phones.Protective coatings on glass molding dies are crucial because molding processes are conducted at molding temperatures that are within the range of glass materials' softening points to deform the glass into the final lens shape [1].Moreover, to be suitable for mass production, molding dies must endure a thermal cycle at temperatures ranging from room temperature to molding temperatures under high pressing loads.Therefore, the requirements of protective coatings are high hardness, smooth surface morphology, high thermal stability, adequate adhesion, long cyclability, and chemical inertness.Following the successful utilization of noble metal alloys [4][5][6][7][8][9][10][11] and carbon films [12,13], transition metal nitride films [14][15][16][17][18][19][20][21][22][23], which offer cost reduction and process control benefits, have become candidates for protective coatings.The oxidation resistance levels of some transition metal nitrides have been improved by the introduction of Si; in particular, improvements to Ti-Si-N [24][25][26] and Zr-Si-N [27][28][29] coatings have been reported.The improved oxidation resistance was attributed to the absence of grain boundaries in the nitride coatings [30].However, the advances in the oxidation resistance were accompanied by a decline in the mechanical properties due to the increase of amorphous volume.In our previous study [31], the nanoindentation hardness values of Zr-Si-N coatings with Si levels of 1-19 at.% increased initially with increasing Si content, peaked, and then dropped to lower levels for higher Si levels, which followed the typical mechanical characteristics of M-Si-N coatings (M: transition metal).However, the coatings with an Si level of 24-30 at.% exhibited the hardness level of Si 3 N 4 , which was higher than that of the coatings with Si levels of 14-19 at.%.The broad reflection of the X-ray diffraction pattern of the amorphous phase located between standard ZrN (111) and orthorhombic Zr 3 N 4 (320) suggested that high Si content can stabilize the nitride in the bonding structure of M 3 N 4 .Therefore, exploring the coating constitutions, which are vital to the coatings' mechanical properties, is imperative.In this study, the effects of sputtering process variables, including the nitrogen flow ratio and substrate holder rotation speed, on the mechanical properties of coatings were investigated.Moreover, the bonding characteristics of the Zr-Si-N coatings with Si levels in the range of 0-30 at.% were examined through X-ray photoelectron spectroscopy.The correlation between the coating constitutions, structural characteristics, and mechanical properties was explored.Finally, the thermal stability and chemical inertness of Zr-Si-N coatings against heat effects and glass materials were evaluated.

Materials and Methods
Three batches of Zr-Si-N coatings were prepared on silicon and cemented carbide (WC-6 wt.%, CB-CERATIZIT, New Taipei City, Taiwan) substrates with dimensions of 20 × 20 × 0.525 mm 3 and 20 × 20 × 3.5 mm 3 , respectively, at room temperature through reactive direct current magnetron cosputtering.The sputtering equipment and cosputtering processes were described in detail in a previous study [32].As illustrated in our previous study [31], Batch I was prepared using various sputter powers.The main process variables for Batches II and III were the nitrogen flow ratio and substrate holder rotation speed, respectively.The evaluations on thermal stability and chemical inertness of Zr-Si-N coatings against SiO 2 -B 2 O 3 -BaO-based glass plates (L-BAL42, Tg: 506 • C, Hk: 590, OHARA, Kanagawa, Japan) were conducted in a quartz tube furnace to simulate glass molding in thermal cycle annealing in a continuous flow of a 15-ppm O 2 -N 2 atmosphere.The glass plates with dimensions of 9.4 × 9.26 × 6.7 mm 3 were placed on the samples during thermal cycle annealing, which involves annealing at 270 • C and 600 • C and maintaining the glasses at 600 • C ± 10 • C for 1 min/cycle [33].The samples were removed from the furnace every 50 thermal cycles for surface observations using an optical microscope (OM, BX-51, Olympus, Tokyo, Japan).
Chemical composition analysis was conducted by using a field-emission electron probe microanalyzer (FE-EPMA, JXA-8500F, JEOL, Akishima, Japan) on the surface of the samples.The standard deviations for chemical composition data were calculated from 3 measurements made at different locations on one sample.Thickness evaluation on cross-sectional images of the coatings was performed by using a field emission scanning electron microscope (FE-SEM, S4800, Hitachi, Tokyo, Japan) at a 15-kV accelerating voltage.A conventional X-ray diffractometer (XRD, X'Pert PRO MPD, PANalytical, Almelo, The Netherlands) with Cu Kα radiation was adopted to identify the phases of the coatings, using the grazing incidence technique with an incidence angle of 1 • .The Cu Kα radiation was generated from a Cu anode operated at 45 KV and 40 mA.The chemical states of the constituent elements were examined by using an X-ray photoelectron spectroscope (XPS, PHI 1600, PHI, Kanagawa, Japan) with an Mg Kα X-ray beam (energy = 1253.6eV and power = 250 W) operated at 15 kV.The XPS spectra of N 1s, Si 2p, and Zr 3d core levels were recorded.Ar + ion beam of 3 keV was used to sputter the coatings for depth profiling.The nonlinear least squares curve fittings were conducted to deconvolute the spectra.The backgrounds were corrected by using a Shirley function and the peaks were fitted by using Gaussian-Lorentzian functions.To split the 3d 5/2 -3d 3/2 Zr doublets, the I(3d 5/2 ):I(3d 3/2 ) intensity ratio was set to 3:2 because of spin-orbit splitting.The splitting energies were 2.43 eV for Zr 3d doublets [34].The surface nanoindentation hardness and Young's Coatings 2018, 8, 181 3 of 14 modulus of coatings were measured with a nanoindentation tester (TI-900 Triboindenter, Hysitron, Minneapolis, MN, USA).The nanoindenter (TI-0039, Hysitron, Minneapolis, MN, USA) was equipped with a Berkovich diamond probe tip, whose radius was 200 nm in diameter.The applied load was controlled to produce an indentation depth of 80 nm.The loading, holding, and unloading times were 5 s each.The nanoindentation hardness and elastic modulus of each indent were calculated using the Oliver and Pharr method [35].The standard deviations for hardness and elastic modulus data were calculated from 5 measurements made at different locations on one sample.The surface roughness values of the coatings, R a [36], were evaluated by using an atomic force microscope (AFM, Dimension 3100 SPM, NanoScope IIIa, Veeco, Santa Barbara, CA, USA).The scanning area of each image was set at 5 × 5 µm 2 with a scanning rate of 1.0 Hz.The residual stress of the films measured by the curvature method was calculated using Stoney's equation [37].
where σ f is the in-plane stress component in the film, t f is the thickness of the film, E S is the Young's modulus of the Si substrate (130.2GPa), ν S is the Poisson's ratio for the Si substrate (0.279) [38], h S is the thickness of the substrate (525 µm), and R f is the radius of the curvature of the film.The measurements were calibrated using BK7 glass plates with curvatures of 0, −0.1, and +0.1 m −1 ; the deviation was 10%.The curvature measurements were conducted using a scan of 10 nm on the surface by recording the reflection of a laser beam.Each sample was analyzed 10 times in each of the two perpendicular directions.

As-Deposited Zr-Si-N Coatings
Table 1 lists the sputtering variables, chemical compositions, and thicknesses of the Zr-Si-N coatings prepared in this study.The sputtering times were controlled to deposit coatings with thicknesses ranging from 890 to 1080 nm; therefore the indentation depth of 80 nm fitted the 1/10 rule for determining the mechanical properties of the coatings.The oxygen contents in the Zr-Si-N coatings were 0.8-1.1 at.%.The samples could be designated in the form Zr x Si y N (100-x−y) (f,Rx), where f is the (N 2 /(N 2 + Ar)) flow ratio and Rx is the substrate holder rotation speed (x rpm) in the sputtering process.Figure 1 illustrates the XRD patterns of the as-deposited Batch-II Zr-Si-N coatings prepared using sputter powers of W Zr = 100 W and W Si = 100 W, a substrate holder rotation speed of 5 rpm, and various (N 2 /(N 2 + Ar)) flow ratios ranging from 0.1 to 0.5.All the Batch II Zr-Si-N coatings with a high Si content of 30-33 at.% exhibited an X-ray amorphous phase and similar chemical compositions.The deposition rate decreased from 10.8, to 8.8, to 7.2, to 6.1, and to 5.1 nm/min as the (N 2 /(N 2 + Ar)) flow ratio was increased from 0.1, to 0.2, to 0.3, to 0.4, and to 0.5, respectively.Moreover, the Batch III Zr-Si-N coatings prepared using sputter powers of W Zr = 100 W and W Si = 100 W, a substrate holder rotation speed of 1-30 rpm, and a (N 2 /(N 2 + Ar)) flow ratio of 0.4 also exhibited similar chemical compositions (31-37 at.%Si), a deposition rate of 5.9-6.9nm/min, and an X-ray amorphous phase (not discussed in this paper).Figure 2 illustrates the ternary diagram of the phase distribution of all the Zr-Si-N coatings, including the Batch I coatings prepared using various sputtering powers, a substrate holder rotation speed of 5 rpm, and a (N 2 /(N 2 + Ar)) flow ratio of 0.4, as described in our previous study [31].These coatings were classified into three phase types: face-centered cubic (f.c.c.), amorphous, and f.c.c. and amorphous mixed phases.Figure 3a shows the relationship between the nanoindentation hardness and residual stress of the Zr-Si-N coatings.In each of the three coating types, the nanoindentation hardness levels exhibited decreasing tendencies as the residual stress varied from compressive toward tensile.Figure 3b shows the relationship between the nanoindentation hardness and Si content of the Zr-Si-N coatings; these X-ray amorphous-phase coatings with a high Si content of 30-37 at.% exhibited a high hardness level, which was similar to that of X-ray amorphous-phase coatings with an Si content of 14-24 at.%.The bonding characteristics of the X-ray amorphous-phase coatings exhibiting divergent mechanical properties were further analyzed.Because the hardness levels of the moldable optical glasses ranged from 3.2 to 7.0 GPa, the protective coatings on the glass molding dies exhibiting a hardness level higher than 10 GPa were preferred [10].Therefore, Zr-Si-N coatings with a high Si content of 30 at.% exhibiting nanoindentation hardness higher than 14.4 GPa should be suitable for protective coatings.

XPS Study of Zr-Si-N Coatings
In a previous study [31], the low-Si-content (0-2 at.%)Zr-Si-N coatings exhibited an f.c.c.structure, whereas the medium-Si-content (6-8 at.%) coatings exhibited a mixture of f.c.c. and amorphous phases, and the high-Si-content (14-37 at.%) coatings exhibited X-ray amorphous structures.Figure 4 shows the XRD reflections of Zr58Si2N40(0.4,R5),Zr52Si8N40(0.4,R5),and Zr22Si30N48(0.4,R5) coatings, respectively representing the aforementioned three classifications.Figure 5 shows the XPS depth profiles of Zr 3d, Si 2p, and N 1s core levels of the as-deposited Zr22Si30N48(0.4,R5) coatings.The profiles of each element at a depth range of 10-70 nm were similar, whereas the profiles on the free surface exhibited deviations caused by the contamination from O. The oxygen content of the as-deposited Zr22Si30N48(0.4,R5) coatings was 0.8 at.%, examined from the surface of the samples by using an FE-EPMA.Figure 6a

XPS Study of Zr-Si-N Coatings
In a previous study [31], the low-Si-content (0-2 at.%)Zr-Si-N coatings exhibited an f.c.c.structure, whereas the medium-Si-content (6-8 at.%) coatings exhibited a mixture of f.c.c. and amorphous phases, and the high-Si-content (14-37 at.%) coatings exhibited X-ray amorphous structures.Figure 4 shows the XRD reflections of Zr58Si2N40(0.4,R5),Zr52Si8N40(0.4,R5),and Zr22Si30N48(0.4,R5) coatings, respectively representing the aforementioned three classifications.Figure 5 shows the XPS depth profiles of Zr 3d, Si 2p, and N 1s core levels of the as-deposited Zr22Si30N48(0.4,R5) coatings.The profiles of each element at a depth range of 10-70 nm were similar, whereas the profiles on the free surface exhibited deviations caused by the contamination from O. The oxygen content of the as-deposited Zr22Si30N48(0.4,R5) coatings was 0.8 at.%, examined from the surface of the samples by using an FE-EPMA.Figure 6a     Table 2 lists all the binding energies for the bonds from ZrN, Zr3N4, and Si3N4 compounds in the Zr-Si-N coatings.The binding energies of Zr 3d5/2 related to Zr-N bonds for ZrN and Zr3N4  Table 2 lists all the binding energies for the bonds from ZrN, Zr3N4, and Si3N4 compounds in the Zr-Si-N coatings.The binding energies of Zr 3d5/2 related to Zr-N bonds for ZrN and Zr3N4 Table 2 lists all the binding energies for the bonds from ZrN, Zr 3 N 4 , and Si 3 N 4 compounds in the Zr-Si-N coatings.The binding energies of Zr 3d 5/2 related to Zr-N bonds for ZrN and Zr 3 N 4 compounds were in the range of 179.14-180.22 and 180.75-181.61eV, respectively, which were comparable to the reported values of 179.6 eV for ZrN x and 181.0 eV for ZrN 1+x [39].Figure 7a shows that the Si 2p of Zr 22 Si 30 N 48 (0.4,R5) coatings comprised two signals, 98.51 ± 0.11 and 100.59 ± 0.13 eV for free Si and Si-N bonds, respectively.The Si substrate without the aforementioned coatings exhibited a Si 2p signal of 99.35 ± 0.01 eV.Choi et al. [25] reported that free Si at a binding energy of 99.3 eV was observed for Ti-Si-N coatings with an Si content >17 at.% because of the deficiency of N. Figure 7b shows that the Si 2p of Zr 52 Si 8 N 40 (0.4,R5) coatings comprised 98.92 and 100.68 eV signals for free Si and Si-N bonds, respectively.Because the Si content was 2 at.%only for the Zr 58 Si 2 N 40 (0.4,R5) coatings, the Si signal was undetectable because of the analysis limitation.The binding energies of Si 2p related to free Si and Si-N bonds for Si 3 N 4 compound were in the range of 98.41-98.92and 100.59-100.89eV, respectively.The latter value exhibited a lower correlation to the reported value of 102.0 eV for Zr 3 N 4 film [39].Figure 8 shows that N 1s of Zr 22 Si 30 N 48 (0.4,R5) coatings comprised signals of 396.97 ± 0.11, 396.13 ± 0.12, and 397.94 ± 0.18 eV for N-Zr bond in ZrN, N-Zr bond in Zr 3 N 4 , and N-Si bond in Si 3 N 4 , respectively.The binding energies of N 1s of all the Zr-Si-N coatings related to N-Zr in ZrN, N-Zr in Zr 3 N 4 , and N-Si in Si 3 N 4 were in the range of 396.87-397.05,396.03-396.20,and 397.94-398.58eV, respectively, which were higher than the reported values of 396.3, 395.4,and 397.7 eV [39].Figure 9 shows the variations in bond characteristics for various Si levels of Zr-Si-N(0.4,R5)coatings.Figure 9a,c show that Zr and N were likely to form a Zr 3 N 4 compound as the Si content in the coatings increased, whereas Si formed Si-N bonds with increasing Si content in the coatings (Figure 9b).Thus, the bond characteristics of Zr 28 Si 24 N 48 (0.4,R5) and Zr 22 Si 30 N 48 (0.4,R5) coatings are Zr 3 N 4 -and Si 3 N 4 -dominated; therefore, the Zr-Si-N coatings with higher Si content of 24-30 at.% exhibited the hardness of Si 3 N 4 at 18-19 GPa [40][41][42].Figure 9 shows the variations in bond characteristics for various Si levels of Zr-Si-N(0.4,R5)coatings.Figure 9a,c show that Zr and N were likely to form a Zr3N4 compound as the Si content in the coatings increased, whereas Si formed Si-N bonds with increasing Si content in the coatings (Figure 9b).Thus, the bond characteristics of Zr28Si24N48(0.4,R5) and Zr22Si30N48(0.4,R5) coatings are Zr3N4-and Si3N4-dominated; therefore, the Zr-Si-N coatings with higher Si content of 24-30 at.% exhibited the hardness of Si3N4 at 18-19 GPa [40][41][42].

Thermal Stability and Chemical Inertness of Zr-Si-N Coatings
In our previous study [31], high-Si-content (15-30 at.%)Zr-Si-N(0.4,R5)coatings exhibited oxidation resistance levels superior to those of low-and medium-Si-content coatings through examination of their oxide layer thicknesses after they were annealed at 600 °C in 1% O2-99% Ar for up to 100 h.The improvement of oxidation resistance was attributed to the formation of amorphous Si-Zr-O oxide scales, which were restricted following oxygen diffusion; thus, the mechanical properties of the high-Si-content (15-30 at.%)Zr-Si-N coatings were similar to those of as-deposited coatings.In the glass molding process, the molded products transfer the surface quality (figure and roughness) from the molding dies.Therefore, a coating roughness maintained at a nanoscale over a long lifetime is preferred.Table 3 shows the surface roughness variations of Zr-Si-N(0.4,R5)coatings during thermal cycle annealing (270-600 °C) in a realistic molding atmosphere (15-ppm O2-N2).The inner positions of the coatings indicated the area contacted SiO2-B2O3-BaO-based glass plates during thermal cycle annealing.The chemical inertness of the coatings against glass was evaluated by the presence of surface damage, such as scraps or dips [10], and flaked or island oxides [21], which consecutively result in roughness variation.The surface roughness variations on the outer positions indicated the thermal stability of the coatings during the glass molding process.The as-deposited Zr-Si-N(0.4,R5)coatings prepared on Si substrates exhibited a surface roughness of 0.3-1.0nm.The surfaces of the outer positions (noncontact area in Figure 10) of low-Si-content Zr60N40(0.4,R5)and Zr58Si2N40(0.4,R5)coatings exhibited severely circular buckle formation following detachment after 50 thermal cycles, whereas black dips exposing the Si substrate were observed in the inner positions (contact area in Figure 10), which implied sticking and detachment.The Zr52Si8N40(0.4,R5) and Zr44Si14N42(0.4,R5) coatings exhibited similar dips in the contact area after 50 thermal cycles, whereas a low surface roughness level of 0.4-0.7 nm was maintained in the noncontact area after 250 cycles.The Zr35Si15N50(0.4,R5) and Zr34Si19N47(0.4,R5) coatings exhibited dips in the contact area after 250 thermal cycles, whereas a low surface roughness level of 0.6-0.7 nm was maintained in their noncontact area after 250 cycles.Undetached parts of the contact area of the Zr35Si15N50(0.4,R5) and Zr34Si19N47(0.4,R5) coatings exhibited roughness values of 4.0 and 2.1 nm, respectively.The Zr28Si24N48(0.4,R5) coatings maintained a smooth surface in the contact and noncontact areas after 250 cycles; however, dips occurred after 500 thermal cycles even though the surface roughness levels of the undetached part of the contact area and the noncontact area were 0.7 and 0.5 nm, respectively.For the amorphous Zr-Si-N(0.4,R5)coatings (14-24 at.%Si), a low surface roughness level of 0.5-0.7 nm was maintained in the noncontact area after 750 cycles.Therefore, the X-ray amorphous-phase Zr-Si-N coatings exhibited high thermal stability in the glass molding process, but their chemical inertness was relatively insufficient.

Thermal Stability and Chemical Inertness of Zr-Si-N Coatings
In our previous study [31], high-Si-content (15-30 at.%)Zr-Si-N(0.4,R5)coatings exhibited oxidation resistance levels superior to those of low-and medium-Si-content coatings through examination of their oxide layer thicknesses after they were annealed at 600 • C in 1% O 2 -99% Ar for up to 100 h.The improvement of oxidation resistance was attributed to the formation of amorphous Si-Zr-O oxide scales, which were restricted following oxygen diffusion; thus, the mechanical properties of the high-Si-content (15-30 at.%)Zr-Si-N coatings were similar to those of as-deposited coatings.In the glass molding process, the molded products transfer the surface quality (figure and roughness) from the molding dies.Therefore, a coating roughness maintained at a nanoscale over a long lifetime is preferred.Table 3 shows the surface roughness variations of Zr-Si-N(0.4,R5)coatings during thermal cycle annealing (270-600 • C) in a realistic molding atmosphere (15-ppm O 2 -N 2 ).The inner positions of the coatings indicated the area contacted SiO 2 -B 2 O 3 -BaO-based glass plates during thermal cycle annealing.The chemical inertness of the coatings against glass was evaluated by the presence of surface damage, such as scraps or dips [10], and flaked or island oxides [21], which consecutively result in roughness variation.The surface roughness variations on the outer positions indicated the thermal stability of the coatings during the glass molding process.The as-deposited Zr-Si-N(0.4,R5)coatings prepared on Si substrates exhibited a surface roughness of 0.3-1.0nm.The surfaces of the outer positions (noncontact area in Figure 10) of low-Si-content Zr 60 N 40 (0.4,R5) and Zr 58 Si 2 N 40 (0.4,R5) coatings exhibited severely circular buckle formation following detachment after 50 thermal cycles, whereas black dips exposing the Si substrate were observed in the inner positions (contact area in Figure 10), which implied sticking and detachment.The Zr 52 Si 8 N 40 (0.4,R5) and Zr 44 Si 14 N 42 (0.4,R5) coatings exhibited similar dips in the contact area after 50 thermal cycles, whereas a low surface roughness level of 0.4-0.7 nm was maintained in the noncontact area after 250 cycles.The Zr 35 Si 15 N 50 (0.4,R5) and Zr 34 Si 19 N 47 (0.4,R5) coatings exhibited dips in the contact area after 250 thermal cycles, whereas a low surface roughness level of 0.6-0.7 nm was maintained in their noncontact area after 250 cycles.Undetached parts of the contact area of the Zr 35 Si 15 N 50 (0.4,R5) and Zr 34 Si 19 N 47 (0.4,R5) coatings exhibited roughness values of 4.0 and 2.1 nm, respectively.The Zr 28 Si 24 N 48 (0.4,R5) coatings maintained a smooth surface in the contact and noncontact areas after 250 cycles; however, dips occurred after 500 thermal cycles even though the surface roughness levels of the undetached part of the contact area and the noncontact area were 0.7 and 0.5 nm, respectively.For the amorphous Zr-Si-N(0.4,R5)coatings (14-24 at.%Si), a low surface roughness level of 0.5-0.7 nm was maintained in the noncontact area after 750 cycles.Therefore, the X-ray amorphous-phase Zr-Si-N coatings exhibited high thermal stability in the glass molding process, but their chemical inertness was relatively insufficient.Cemented carbide is a representative die material for glass molding.A Ti interlayer of 100 nm was inserted to fabricate the Zr-Si-N/Ti/WC assembly, which prevented buckle formation during repeated thermal cycle annealing [21].The Zr22Si30N48(0.4,R5) process was conducted again to fabricate a Zr22Si29N49/Ti/WC assembly; this assembly exhibited a surface roughness of 1.5 nm in the as-deposited state, which was higher than those of the Zr-Si-N(0.4,R5)coatings prepared on Si wafers.The Zr22Si29N49/Ti/WC assembly maintained a smooth surface in the contact and noncontact areas after 250 and 400 thermal cycles; however, black dips of the Zr22Si29N49/Ti coatings occurred after 500 thermal cycles (Figure 11).No buckle formation was observed.The 450-cycle-treated sample showed no sticking marks.The as-prepared Zr22Si29N49/Ti/WC assembly exhibited a surface roughness of 1.5 nm, which was lower than that of the Ta26Si16N58/Ti/WC assembly (2.9 nm), indicating a higher chemical inertness of 1400 thermal cycles against SiO2-B2O3-BaO-based glass [21].

Conclusions
The Zr-Si-N coatings with an Si content higher than 14 at.%exhibited an X-ray amorphous phase.Moreover, the nanoindentation hardness level of the Zr-Si-N coatings with an Si content of >30 at.% was >14.4 GPa, which was higher than those of the coatings with an Si content of 14-24 at.%; this was attributed to the variation of bonding characteristics.The structure varied from Cemented carbide is a representative die material for glass molding.A Ti interlayer of 100 nm was inserted to fabricate the Zr-Si-N/Ti/WC assembly, which prevented buckle formation during repeated thermal cycle annealing [21].The Zr 22 Si 30 N 48 (0.4,R5) process was conducted again to fabricate a Zr 22 Si 29 N 49 /Ti/WC assembly; this assembly exhibited a surface roughness of 1.5 nm in the as-deposited state, which was higher than those of the Zr-Si-N(0.4,R5)coatings prepared on Si wafers.The Zr 22 Si 29 N 49 /Ti/WC assembly maintained a smooth surface in the contact and noncontact areas after 250 and 400 thermal cycles; however, black dips of the Zr 22 Si 29 N 49 /Ti coatings occurred after 500 thermal cycles (Figure 11).No buckle formation was observed.The 450-cycle-treated sample showed no sticking marks.The as-prepared Zr 22 Si 29 N 49 /Ti/WC assembly exhibited a surface roughness of 1.5 nm, which was lower than that of the Ta 26 Si 16 N 58 /Ti/WC assembly (2.9 nm), indicating a higher chemical inertness of 1400 thermal cycles against SiO 2 -B 2 O 3 -BaO-based glass [21].Cemented carbide is a representative die material for glass molding.A Ti interlayer of 100 nm was inserted to fabricate the Zr-Si-N/Ti/WC assembly, which prevented buckle formation during repeated thermal cycle annealing [21].The Zr22Si30N48(0.4,R5) process was conducted again to fabricate a Zr22Si29N49/Ti/WC assembly; this assembly exhibited a surface roughness of 1.5 nm in the as-deposited state, which was higher than those of the Zr-Si-N(0.4,R5)coatings prepared on Si wafers.The Zr22Si29N49/Ti/WC assembly maintained a smooth surface in the contact and noncontact areas after 250 and 400 thermal cycles; however, black dips of the Zr22Si29N49/Ti coatings occurred after 500 thermal cycles (Figure 11).No buckle formation was observed.The 450-cycle-treated sample showed no sticking marks.The as-prepared Zr22Si29N49/Ti/WC assembly exhibited a surface roughness of 1.5 nm, which was lower than that of the Ta26Si16N58/Ti/WC assembly (2.9 nm), indicating a higher chemical inertness of 1400 thermal cycles against SiO2-B2O3-BaO-based glass [21].

Conclusions
The Zr-Si-N coatings with an Si content higher than 14 at.%exhibited an X-ray amorphous phase.Moreover, the nanoindentation hardness level of the Zr-Si-N coatings with an Si content of >30 at.% was >14.4 GPa, which was higher than those of the coatings with an Si content of 14-24 at.%; this was attributed to the variation of bonding characteristics.The structure varied from

Figure 1 .
Figure 1.XRD patterns of as-deposited Zr-Si-N coatings prepared on Si substrates using various (N 2 /(N 2 + Ar)) flow ratios, a substrate holder rotation speed of 5 rpm, and sputter powers of W Zr = 100 W and W Si = 100 W.

Figure 3 .
Figure 3. Relationships between nanoindentation hardness and (a) residual stress and (b) Si content of Zr-Si-N coatings.
shows a curve fitting of the Zr profile at a depth of 60 nm of the Zr22Si30N48(0.4,R5)coatings; the Zr profile was split into two sets of doublets, representing Zr-N bonds for two compounds, ZrN and Zr3N4.The Zr 3d5/2 signals were determined at 180.22 ± 0.03 and 181.01 ± 0.06 eV for ZrN and Zr3N4, respectively, which exhibited a count ratio of 46:54.Figure 6b,c show the curve fitting of the Zr profiles at a depth of 60 nm of the Zr52Si8N40(0.4,R5)and Zr58Si2N40(0.4,R5)coatings, respectively; ZrN was the dominant Zr compound.The Zr 3d5/2 signals were 179.14 and 181.09 eV for ZrN and Zr3N4 in the Zr52Si8N40(0.4,R5)coatings, respectively, whereas these signals were 179.30 and 181.61 eV for ZrN and Zr3N4 in the Zr58Si2N40(0.4,R5)coatings, respectively.

Figure 3 .
Figure 3. Relationships between nanoindentation hardness and (a) residual stress and (b) Si content of Zr-Si-N coatings.

Figure 4 Figure 3 .
Figure 3. Relationships between nanoindentation hardness and (a) residual stress and (b) Si content of Zr-Si-N coatings.
shows a curve fitting of the Zr profile at a depth of 60 nm of the Zr22Si30N48(0.4,R5)coatings; the Zr profile was split into two sets of doublets, representing Zr-N bonds for two compounds, ZrN and Zr3N4.The Zr 3d5/2 signals were determined at 180.22 ± 0.03 and 181.01 ± 0.06 eV for ZrN and Zr3N4, respectively, which exhibited a count ratio of 46:54.Figure 6b,c show the curve fitting of the Zr profiles at a depth of 60 nm of the Zr52Si8N40(0.4,R5)and Zr58Si2N40(0.4,R5)coatings, respectively; ZrN was the dominant Zr compound.The Zr 3d5/2 signals were 179.14 and 181.09 eV for ZrN and Zr3N4 in the Zr52Si8N40(0.4,R5)coatings, respectively, whereas these signals were 179.30 and 181.61 eV for ZrN and Zr3N4 in the Zr58Si2N40(0.4,R5)coatings, respectively.

Figure 8 .
Figure 8. XPS profiles of N 1s core levels of Zr22Si30N48(0.4,R5) coatings at a depth of 60 nm.Figure 8. XPS profiles of N 1s core levels of Zr 22 Si 30 N 48 (0.4,R5) coatings at a depth of 60 nm.

Figure 8 .
Figure 8. XPS profiles of N 1s core levels of Zr22Si30N48(0.4,R5) coatings at a depth of 60 nm.Figure 8. XPS profiles of N 1s core levels of Zr 22 Si 30 N 48 (0.4,R5) coatings at a depth of 60 nm.

Figure 11 .
Figure 11.Surface morphology of the contact area of the Zr22Si29N49/Ti/WC assembly after 500 thermal cycles.

Figure 11 .
Figure 11.Surface morphology of the contact area of the Zr22Si29N49/Ti/WC assembly after 500 thermal cycles.

Figure 11 .
Figure 11.Surface morphology of the contact area of the Zr 22 Si 29 N 49 /Ti/WC assembly after 500 thermal cycles.

eV) Zr 3d 5/2 Si 2p N 1s ZrN Zr 3 N 4 Si 3 N 4 Free Si ZrN Zr 3 N 4 Si 3 N 4 Zr 60
[39] coatings with an Si content >17 at.% because of the deficiency of N. Figure7bshows that the Si 2p of Zr52Si8N40(0.4,R5)coatingscomprised98.92 and 100.68 eV signals for free Si and Si-N bonds, respectively.Because the Si content was 2 at.%only for the Zr58Si2N40(0.4,R5)coatings,theSisignalwasundetectablebecause of the analysis limitation.The binding energies of Si 2p related to free Si and Si-N bonds for Si3N4 compound were in the range of 98.41-98.92and100.59-100.89eV,respectively.The latter value exhibited a lower correlation to the reported value of 102.0 eV for Zr3N4 film[39].Figure8shows that N 1s of Zr22Si30N48(0.4,R5) coatings comprised signals of 396.97 ± 0.11, 396.13 ± 0.12, and 397.94 ± 0.18 eV for N-Zr bond in ZrN, N-Zr bond in Zr3N4, and N-Si bond in Si3N4, respectively.The binding energies of N 1s of all the Zr-Si-N coatings related to N-Zr in ZrN, N-Zr in Zr3N4, and N-Si in Si3N4 were in the range of 396.87-397.05,396.03-396.20,and397.94-398.58eV,respectively,which were higher than the reported values of 396.3, 395.4,and 397.7 eV[39].